Crop water stress index for watermelon

This study was conducted to determine the suitability of a crop water stress index (CWSI) to schedule irrigation for watermelon (Citrullus vulgaris) grown with trickle irrigation. The effects of five irrigation levels (100, 75, 50, 25 and 0% replenishment of soil water depleted from 0.90 m soil profile depth) on watermelon yields and resulting CWSI were investigated. The highest yield and water use was obtained under fully irrigated conditions (100% replenishment of soil water depleted) in 2 years. The CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures and vapor pressure deficit values for five irrigation levels. The trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Unlike the yield, CWSI increased with increased soil water deficit. An average CWSI of about 0.41 before irrigation produced the maximum yield. The yield was directly correlated with mean CWSI values and the linear equation 'Y = 91.143 - 66.077 CWSI' can be used for yield prediction. The CWSI value was useful for evaluating crop water stress in watermelon and should be useful for timing irrigation and predicting yield. (C) 2003 Elsevier Science B.V. All rights reserved.